The present invention relates generally to desiccation of a material, and, more particularly to a process and apparatus for accurately and repeatably desiccating material which requires strict temperature control during the desiccation process.
Desiccation techniques and apparatuses are well-known in the art and typically consist of a desiccation chamber and a trap chamber. The desiccation chamber is often provided with racks which support the material to be desiccated. The racks themselves are often provided with tubes which carry a heat-carrying fluid to heat, or to draw heat away from, the material as appropriate. The trap chamber is provided with a trap which is cooled during the desiccation process. The chambers are typically connected by means of a conduit through which water vapor passes from the desiccation chamber to the trap chamber during the desiccation process.
To begin desiccation, the material is placed upon the racks and brought to a very low temperature, typically on the order -45.degree. C. The trap is brought to a similarly low temperature. After the material has adequately cooled throughout its interior, the temperature of the racks is raised to a temperature just below the eutectic of the material. The pressure within both the desiccation chamber and the trap chamber is reduced to a few pascals. Under this low pressure, moisture within the material sublimes, with the vapor moving toward the colder trap, which captures and retains the moisture. After most of the moisture has been removed from the material, the racks are heated to remove the last traces of water bound within the material. The material is then adequately desiccated and ready for use.
One draw-back with prior art desiccation apparatuses and techniques is the temperature gradient within the desiccation chamber. Although the temperature of the racks are accurately controlled with the heat-carrying fluid, the walls of the desiccation chamber remain significantly warmer than the racks. Due to this temperature gradient, the walls of the desiccation chamber tend to radiate heat toward the edges of the racks. This radiated heat warms the material placed at the edges of the rack more than material placed at the center of the racks, throughout the cooling process. Similarly, as the racks are heated above room temperature, the walls of the desiccation chamber remain cooler than the racks, absorbing heat more readily from the edges of the racks than from the center of the racks. Both of these factors co-act to create inconsistent desiccation between material at the edges of the racks and material at the centers of the racks. While such temperature variances may be acceptable for some products, products such as pharmaceuticals require highly specific and consistent desiccation temperatures to create materials within desired specifications.
Another problem associated with prior art desiccation apparatuses and methods involves sterilization of the apparatuses. Sterilization typically involves adding a sterilizing material such as hydrogen peroxide to both the desiccation chamber and the trap chamber and elevating the temperatures within both chambers to aid in the sterilization process. The aforementioned temperature gradient between the interior of the chambers and the walls of the chambers leads to inconsistent sterilization. This temperature variance often leads to lengthy sterilization processes required to assure every portion of both chambers has reached an adequate temperature for a sufficient length of time.
The difficulties encountered in the prior art discussed hereinabove are substantially eliminated by the present invention.